But women are his most urgent target. Unlike the other core groups, women are undecided, rather than merely unmotivated. And there are signs in parts of the country that they are open to defecting to the Republicans, potentially defying the long-standing "gender gap" that has skewed heavily toward Democratic candidates.

In the highly competitive Colorado Senate race, women are divided almost evenly between Democratic Sen. Michael Bennet and his Republican challenger, Ken Buck. In Missouri, female voters are not giving any measurable boost to Democratic Senate candidate Robin Carnahan, who is trailing Republican Rep. Roy Blunt. And in New Hampshire, Republican Senate candidate Kelly Ayotte is actually ahead among women by 10 percentage points, one of several factors in her lead overall.

In the House races, where women have sided with Democrats by an average of nine points since 1976, they are now about evenly split between Democrats and Republicans, in the latest Washington Post-ABC News poll. That is a sharp drop-off from just four years ago, when women chose Democrats by a large 12-point margin and put them in the majority.

Of course, the news is not good for Democrats almost everywhere - and certainly much worse among white men, who are embracing Republican candidates by a greater proportion than ever before. But the women matter more: As a whole, men lean Republican, while women usually act as a counterbalance for Democrats.

"Women are not a shrinking piece of the electorate. They're a shrinking piece of the Democratic pie," Lee Miringoff, director of the Marist Institute for Public Opinion, said, refuting the notion that female voters are simply unmotivated like the rest of the Democratic base. Celinda Lake, a Democratic pollster, said Democrats are seeing an erosion with women who did not attend college, especially because of the economy.

"They do not think the administration's economic policies are working for their families, and worry about the priorities of this administration, and wonder if they get it," Lake said.

To counteract the trend, Democrats have released a torrent of gender-based negative ads in recent weeks - attacking male Republican House candidates for bad behavior, underscoring Republican candidates' opposition to legalized abortion and other women's health issues, and, in the Kentucky Senate race, airing an ad that asks, among other things: "Why did Rand Paul once tie a woman up?"

The White House is also stepping in.

On Thursday, President Obama will hold an official event in Seattle targeting women on economic issues, before campaigning with Sen. Patty Murray, who has had an advantage among women voters since first being elected in 1992 as a "mom in tennis shoes." Obama is also sending out senior female members of the administration to talk about economic matters, spokeswoman Jen Psaki said. The idea, she said, is to remind female voters that "there are millions of women who've benefited" from Obama's small business programs, with more benefits on the way from a new consumer protection agency and health-care reform. First lady Michelle Obama's recent foray onto the campaign trail has been aimed at women as well.

Democrats argue that the gender gap in their favor isn't disappearing but simply becoming less of a sure thing. Although it has failed to rescue Senate candidates in Missouri, New Hampshire or Wisconsin so far, it is still holding strong for Murray in Washington, as well as for Gov. Joe Manchin in West Virginia and Chris Coons in Delaware. In Nevada, where Senate Majority Leader Harry M. Reid is locked in a close race with Republican challenger Sharron Angle, there is a Democratic advantage among female voters, albeit not as pronounced as it has been in the past.

"The firewall that was six feet high is now four feet high," Brad Coker of Mason-Dixon Polling & Research, which has conducted polling in Nevada and elsewhere, said. "[Democrats] still do better with women than Republicans do, but the gap between what Republicans and Democrats get with women has narrowed in favor of Republicans."